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John

08/04/2017 at 19:59
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Let R and S be points on the sides BC and AC , respectively, of ΔABC , and let P be the intersection of AR and BS . Determine the area of ΔABC if the areas of ΔAPS , ΔAPB , and ΔBPR are 5, 6, and 7, respectively


area


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    An Duong 09/04/2017 at 07:31

    A B C R S P 5 6 7 M N x y

    We have \(\dfrac{SP}{PB}=\dfrac{area\left(APS\right)}{area\left(ABP\right)}=\dfrac{5}{6}\)

    Call the area of PSR be x, the area of CSR be y, we have:

      \(\dfrac{area\left(PSR\right)}{area\left(PBR\right)}=\dfrac{SP}{PB}=\dfrac{5}{6}\)

    \(\Rightarrow\dfrac{x}{7}=\dfrac{5}{6}\) \(\Rightarrow x=\dfrac{35}{6}\)

    \(\dfrac{BR}{CR}=\dfrac{area\left(BSR\right)}{area\left(CRS\right)}=\dfrac{7+x}{y}\)     (1)

    \(\dfrac{BR}{CR}=\dfrac{area\left(ABR\right)}{area\left(ACR\right)}=\dfrac{13}{x+y+5}\)   (2)

    (1), (2) => \(\dfrac{7+x}{y}=\dfrac{13}{x+y+5}\)

    \(\Rightarrow y=\dfrac{\left(7+x\right)\left(5+x\right)}{6-x}=\dfrac{5005}{6}\)

    So, \(area\left(ABC\right)=5+6+7+x+y\)

                                 \(=5+6+7+\dfrac{35}{6}+\dfrac{5005}{6}=858\)

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    FA KAKALOTS 28/01/2018 at 22:09

    A B C R S P 5 6 7 M N x y

    We have SPPB=area(APS)area(ABP)=56

    Call the area of PSR be x, the area of CSR be y, we have:

      area(PSR)area(PBR)=SPPB=56

    ⇒x7=56

     ⇒x=356

    BRCR=area(BSR)area(CRS)=7+xy

         (1)

    BRCR=area(ABR)area(ACR)=13x+y+5

       (2)

    (1), (2) => 7+xy=13x+y+5

    ⇒y=(7+x)(5+x)6−x=50056

    So, area(ABC)=5+6+7+x+y

                                 =5+6+7+356+50056=858


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